---
page_title: Backend Configuration - Configuration Language
---

# Backend Configuration

A backend defines where Terraform stores its [state](/language/state) data files.

Terraform uses persisted state data to keep track of the resources it manages. Most non-trivial Terraform configurations either [integrate with Terraform Cloud](/language/settings/terraform-cloud) or use a backend to store state remotely. This lets multiple people access the state data and work together on that collection of infrastructure resources.

This page describes how to configure a backend by adding the [`backend` block](#using-a-backend-block) to your configuration.

-> **Note:** In Terraform versions before 1.1.0, we classified backends as standard or enhanced. The enhanced label differentiated the [`remote` backend](/language/settings/backends/remote), which could both store state and perform Terraform operations. This classification has been removed. Refer to [Using Terraform Cloud](/cli/cloud) for details about storing state, executing remote operations, and using Terraform Cloud directly from Terraform.

## Available Backends

By default, Terraform uses a backend called [`local`](/language/settings/backends/local), which stores state as a local file on disk. You can also configure one of the built-in backends listed in the documentation sidebar.

Some of these backends act like plain remote disks for state files, while others support locking the state while operations are being performed. This helps prevent conflicts and inconsistencies. The built-in backends listed are the only backends. You cannot load additional backends as plugins.

## Using a Backend Block

You do not need to configure a backend when using Terraform Cloud because
Terraform Cloud automatically manages state in the workspaces associated with your configuration. If your configuration includes a [`cloud` block](/language/settings/terraform-cloud), it cannot include a `backend` block.

To configure a backend, add a nested `backend` block within the top-level
`terraform` block. The following example configures the `remote` backend.

```hcl
terraform {
  backend "remote" {
    organization = "example_corp"

    workspaces {
      name = "my-app-prod"
    }
  }
}
```

There are some important limitations on backend configuration:

- A configuration can only provide one backend block.
- A backend block cannot refer to named values (like input variables, locals, or data source attributes).

### Credentials and Sensitive Data

Backends store state in a remote service, which allows multiple people to access it. Accessing remote state generally requires access credentials, since state data contains extremely sensitive information.

!> **Warning:**  We recommend using environment variables to supply credentials and other sensitive data. If you use `-backend-config` or hardcode these values directly in your configuration, Terraform will include these values in both the `.terraform` subdirectory and in plan files. This can leak sensitive credentials.

Terraform writes the backend configuration in plain text in two separate files.
- The `.terraform/terraform.tfstate` file contains the backend configuration for the current working directory.
- All plan files capture the information in `.terraform/terraform.tfstate` at the time the plan was created. This helps ensure Terraform is applying the plan to correct set of infrastructure.

When applying a plan that you previously saved to a file, Terraform uses the backend configuration stored in that file instead of the current backend settings. If that configuration contains time-limited credentials, they may expire before you finish applying the plan. Use environment variables to pass credentials when you need to use different values between the plan and apply steps.

### Backend Types

The block label of the backend block (`"remote"`, in the example above) indicates which backend type to use. Terraform has a built-in selection of backends, and the configured backend must be available in the version of Terraform you are using.

The arguments used in the block's body are specific to the chosen backend type; they configure where and how the backend will store the configuration's state, and in some cases configure other behavior.

Some backends allow providing access credentials directly as part of the configuration for use in unusual situations, for pragmatic reasons. However, in normal use we _do not_ recommend including access credentials as part of the backend configuration. Instead, leave those arguments completely unset and provide credentials via the credentials files or environment variables that are conventional for the target system, as described in the documentation for each backend.

Refer to the list of backend types in the navigation sidebar for details about each supported backend type and its configuration arguments.

### Default Backend

If a configuration includes no backend block, Terraform defaults to using the `local` backend, which stores state as a plain file in the current working directory.

## Initialization

Whenever a configuration's backend changes, you must run `terraform init` again
to validate and configure the backend before you can perform any plans, applies,
or state operations.

When changing backends, Terraform will give you the option to migrate
your state to the new backend. This lets you adopt backends without losing
any existing state.

To be extra careful, we always recommend manually backing up your state
as well. You can do this by simply copying your `terraform.tfstate` file
to another location. The initialization process should create a backup
as well, but it never hurts to be safe!

## Partial Configuration

You do not need to specify every required argument in the backend configuration.
Omitting certain arguments may be desirable if some arguments are provided
automatically by an automation script running Terraform. When some or all of
the arguments are omitted, we call this a _partial configuration_.

With a partial configuration, the remaining configuration arguments must be
provided as part of [the initialization process](/cli/init).

There are several ways to supply the remaining arguments:

- **File**: A configuration file may be specified via the `init` command line.
  To specify a file, use the `-backend-config=PATH` option when running
  `terraform init`. If the file contains secrets it may be kept in
  a secure data store, such as [Vault](https://www.vaultproject.io/),
  in which case it must be downloaded to the local disk before running Terraform.

- **Command-line key/value pairs**: Key/value pairs can be specified via the
  `init` command line. Note that many shells retain command-line flags in a
  history file, so this isn't recommended for secrets. To specify a single
  key/value pair, use the `-backend-config="KEY=VALUE"` option when running
  `terraform init`.

- **Interactively**: Terraform will interactively ask you for the required
  values, unless interactive input is disabled. Terraform will not prompt for
  optional values.

If backend settings are provided in multiple locations, the top-level
settings are merged such that any command-line options override the settings
in the main configuration and then the command-line options are processed
in order, with later options overriding values set by earlier options.

The final, merged configuration is stored on disk in the `.terraform`
directory, which should be ignored from version control. This means that
sensitive information can be omitted from version control, but it will be
present in plain text on local disk when running Terraform.

When using partial configuration, Terraform requires at a minimum that
an empty backend configuration is specified in one of the root Terraform
configuration files, to specify the backend type. For example:

```hcl
terraform {
  backend "consul" {}
}
```

### File

A backend configuration file has the contents of the `backend` block as
top-level attributes, without the need to wrap it in another `terraform`
or `backend` block:

```hcl
address = "demo.consul.io"
path    = "example_app/terraform_state"
scheme  = "https"
```

`*.backendname.tfbackend` (e.g. `config.consul.tfbackend`) is the recommended
naming pattern. Terraform will not prevent you from using other names but following
this convention will help your editor understand the content and likely provide
better editing experience as a result.

### Command-line key/value pairs

The same settings can alternatively be specified on the command line as
follows:

```
$ terraform init \
    -backend-config="address=demo.consul.io" \
    -backend-config="path=example_app/terraform_state" \
    -backend-config="scheme=https"
```

The Consul backend also requires a Consul access token. Per the recommendation
above of omitting credentials from the configuration and using other mechanisms,
the Consul token would be provided by setting either the `CONSUL_HTTP_TOKEN`
or `CONSUL_HTTP_AUTH` environment variables. See the documentation of your
chosen backend to learn how to provide credentials to it outside of its main
configuration.

## Changing Configuration

You can change your backend configuration at any time. You can change
both the configuration itself as well as the type of backend (for example
from "consul" to "s3").

Terraform will automatically detect any changes in your configuration
and request a [reinitialization](/cli/init). As part of
the reinitialization process, Terraform will ask if you'd like to migrate
your existing state to the new configuration. This allows you to easily
switch from one backend to another.

If you're using multiple [workspaces](/language/state/workspaces),
Terraform can copy all workspaces to the destination. If Terraform detects
you have multiple workspaces, it will ask if this is what you want to do.

If you're just reconfiguring the same backend, Terraform will still ask if you
want to migrate your state. You can respond "no" in this scenario.

## Unconfiguring a Backend

If you no longer want to use any backend, you can simply remove the
configuration from the file. Terraform will detect this like any other
change and prompt you to [reinitialize](/cli/init).

As part of the reinitialization, Terraform will ask if you'd like to migrate
your state back down to normal local state. Once this is complete then
Terraform is back to behaving as it does by default.
